The present invention is comprised in the field of friction materials for brake pads, which, as well known, shall have a composition such as to ensure consistent and reliable performances in a wide range of operative conditions.
In particular, as the disc brake pads for vehicles operate under extreme and hard working conditions, having to satisfy at the same time reliability and a long life, the manufacturers have constantly tried to improve the features and performances of friction materials.
The brake pad is indeed formed of a support base, usually metallic, and of a friction layer composed of various materials. According to the properties and the composition of the friction material, it is possible to promote efficiency (namely the braking force) or the pad life.
In the state of the art the first friction materials for brake pads had a composition containing asbestos. However, also in this field, as soon as the dangerousness of asbestos made its use, at first discouraged, then forbidden, substitutive compounds have been sought.
Replacement materials have been therefore searched which could allow to achieve a product characterized by equal or improved performances with respect to those obtained through the friction material containing asbestos and have been thus developed, for example, friction materials containing steel and various types of metals in variable amounts (such as for example copper, aluminium, zinc, etc.) and comprising, as binding element, thermosetting resins such as phenolic resins as such, and or modified phenolic resins among which the silicon and epoxy acrylic resins.
These thermosetting resins are currently present in the friction materials for brake pads in a percentage of 8-20% by weight with respect to the total weight of the composition of the friction material and are necessary for allowing hot moulding of the braking mixture, ensuring excellent final performances of the brake pad, such as braking capability, resistance to wear and to abrasion, etc.
The use of thermosetting phenolic resins presents however some drawbacks, first of all a problem of environmental sustainability and potential toxicity. It deals, indeed, with resins which may release phenol, formaldehyde and derivatives from the thermo-oxidative degradation, both during processing, and during the use of the end-product. Pursuant to regulation EC 1272/2008, phenol is classified as toxic substance, harmful in case of protracted contact with the skin and mutagenic of class 3. Consequently the search for alternatives for reducing the emission of phenols in the environment is active in all fields.
As a consequence, such a problem occurred also in the field of friction materials: indeed, although each piece of friction materials releases only low quantities of phenols and formaldehyde, overall the quantity of phenols released can become significant, both due to the great number of vehicles on the roads and for the great number of industrial applications using said materials.
A purpose of the present invention is therefore that of identifying a friction material having a composition allowing to satisfy at the same time the required technical specifications, such as the thermo-mechanical ones, ensuring however a high environmental sustainability, overcoming thus the drawbacks of the friction materials containing phenolic resins according to the prior art.
A further purpose of the present invention is the use of such a friction material in brake pads and in further industrial applications.